Overview

In this post we’ll go through how to develop and deploy additional view types beyond the default simple and detailed views in the document library in Share.

The techniques here require Alfresco 4.0.2 or later, or a recent checkout of community HEAD.

The Document Library Component

We won’t go into all the details on how the document library is rendered but it’s a fairly standard webscript-based component with ‘server-side’ resources like FreeMarker files for HTML fragments, Javascript for manipulating the data model, and localization properties files, and ‘client-side’ resources sent to the browser like CSS and Javascript.

While adding a document library view will involve changes to both client-side and server-side tiers, most of our notable changes will be to client-side Javascript files sent to the browser. The server-side webscripts changes are primarily to load and instantiate the client-side objects.

and note that within that directory resources from include/documentlist.* are included by some of the primary files.

DocumentList and DocumentListViewRenderer

The DocumentList Javascript object makes up the bulk of the document library view and is defined in the client-side documentlist.js file along with event handler methods and other display setup. The DocumentList object sets up a YUIDataTable which handles most of the work of AJAX calls, pagination, etc.

Each column in the DataTable is assigned a method which dictates how to render that column given the data row. For example, the DataTable calls DocumentList.fnRenderCellThumbnail for the ‘thumbnail’ column of each row it renders.

The DocumentList also contains a set of registered DocumentListViewRenderers, ‘simple‘ and ‘detailed‘ by default, which do the work of generating the HTML for their view type. In other words, DocumentList.fnRenderCellThumbnail actually determines the current view renderer based on the current viewRendererName and hands off its work to DocumentListViewRenderer.renderCellThumbnail.

This allows developers to create their own objects which extend and override the DocumentListViewRenderer with methods for their specific needs.

For this example our goal will be to add a view which is very similar to the existing detail view but with larger thumbnails.

Steps to Add a View

Define the View

For a new view we need to define a new DocumentListViewRenderer object. That customization could be just a new instance of the base DocumentListViewRenderer with a different name so that alternate CSS is applied and metadata rendered.

The name of the view renderer specified in the constructor is used for CSS class names among other things so a simple example of adding a second detailed view with a larger thumbnail might look like:

new Alfresco.DocumentListViewRenderer("large");

In more complex scenarios you probably want to extend DocumentListViewRenderer in a client-side documentlist-custom.js file, which is what we’ll do in this example.

and we’ll override the renderCellThumbnail method with almost the same code in the detail view, but adding a documents-large CSS class to the thumbnail container and changing the call to generateThumbnailUrl to use the imgpreview thumbnail definition:

Register the View

Once the view renderer has been defined it needs to be registered with the DocumentList object via its registerViewRenderer method. This needs to be done after the DocumentList object has been created and setup, so a good place to perform the registration is after the YUI Bubbling Event postSetupViewRenderers has fired. To register the same view above:

Accessing the View

The user has to be able to navigate to this new view and even though we’ve registered it, the DocumentList needs to know which view renderers are enabled and in what order, both of which are defined in the DocumentList’s options under viewRendererNames. We can add our custom view above to the server-side FreeMarker model:

model.viewRendererNames.push("large");

Note that the name here must match the name of the view renderer constructor.

Not only does this define that the ‘large‘ view is enabled, the navigation buttons are also rendered from this viewRendererNames list, so we’ve taken care of the interface as well.

CSS

Our overridden renderCellThumbnail method above adds the documents-large CSS class so we’ll need to define that, as well as the display of the view selection button. Here’s a portion of the documentlist-custom.css file:

Packaging

There are of course a number of ways this code could be packaged and deployed but this type of customization lends itself particularly well to a share extensibility module which Erik Winlöf and David Draper have blogged about in detail. We’ll assume a standard Maven or Gradle Java project layout for the code, and to keep things simple the example deploys as a Share jar rather than an AMP.

We could place the javascript which creates the new view renderer a number of places, even purely client-side, but as we’ll see in another post it can be handy to have access to the FreeMarker data model so we’ll place it in:

Results

The next time you go to a site’s document library you should see the additional
button for your view and the larger thumbnails:

Since we implemented this as a standard extensibility module you can completely disable it by going to your Share deployment’s module management page at something like http://localhost:8080/share/page/modules/deploy and disable the module.

What’s Next?

I’ll go into more advanced customizations in future posts, but in the meantime, what kind of doclib view are you going to build?

SELECT D.* FROM cmis:document AS D WHERE D.cmis:name LIKE '%Flower%' OR D.cmis:contentStreamFileName LIKE '%Flower%'

was giving me a fit lately, not working at all in RightsPro‘s CMIS plugin which uses OpenCMIS and yielding inconsistent results in CMIS Workbench where re-posting the same query ten times would give the expected result maybe half the time.

Thanks to Florian Müller and this post, it seems as though Alfresco doesn’t always behave as expected when the locale is set in the CMIS session.

Removing the locale session parameters got things working in RightsPro, but I didn’t immediately see an easy way to change the locale in a Workbench session (the log shows that it’s using a default of en_US), and I still don’t know what’s up with the inconsistent results there, perhaps a coincidental caching issue.

This was all using OpenCMIS 0.3 against Alfresco Enterprise 3.3.1 over SSL.

Alfresco has undergone quite a few changes under the hood in version 3.3, including refactoring of the ThumbnailService to make use of the RenditionService, which I had to explore in a recent deep dive to get video working for the thumbnails extension. This is obviously a subject dear to your heart as well or you would have moved on by now.

Alfresco 3.1.

Let’s take a look at how things worked back in the old days, before 3.2 (fuzzy 2009 dream sequence begins…)

You most likely kicked things off with a thumbnail generating URL which would hit a ScriptNode.createThumbnail method which looked up the thumbnailDefinition and called the ThumbnailService with the TransformationOptions contained in the definition.

The ThumbnailService then told the ContentService to perform the transformation which looked up the ContentTransformer from the TransformerRegistry and executed transformer.transform which usually delegated to a RuntimeExec object to perform the actual command line transformation.

If we were to visualize the key elements of that stack for a synchronous video thumbnail creation it would look something like:

Alfresco 3.3.

These Alfresco people don’t mess around. If it’s determined that refactoring should happen, it happens, real damn quick, even if it’s huge. To that end subsystems were rolled out in 3.2 and the RenditionService was introduced in 3.3.

Subsystems. Certain content transformers, like ImageMagick, have been refactored as a subsystem, which is cool. Read the wiki page to get the full story but in short it’s a much more flexible architecture.

The ffmpeg video transformer contained in the latest release of the thumbnails extension follows this precedence and has been refactored as a subsystem, so there.

RenditionService. I wouldn’t say I hate it, but this package should be wary of eating crackers in bed, or maybe I’m just not familiar enough with it yet.

The new rendition service utilizes RenditionDefinitions which require that any TransformationOptions be ‘serialized’ into a parameter map, which are then reassembled into TransformationOptions objects before being passed to the ContentTransformer. I suppose this is done to make it easier to do things like hand renditions off to another server in a cluster, but it’s a bit of a pain in the ass for developers.

So, back to our synchronous video thumbnail creation scenario (deep breath), the ThumbnailService now creates a RenditionDefinition which it passes to the RenditionService which wraps things up in a PerformRenditionActionExecuter that gets passed to the ActionService. The PerformRenditionActionExecuter calls the ActionService again which loads the RenderingEngine from the spring ApplicationContext. A RenderingEngine is itself an ActionExecuter so the ActionService calls execute which calls render which proceeds to rebuild the TransformationOptions object needed by the ContentService to get the proper ContentTransformer so transformer.transform can use a RuntimeExec object to perform the actual command line transformation.

A while ago we submitted an issue to Alfresco suggesting TransformationOptions which contain distinct target AND source options so that one could for example specify that all ‘doclib’ thumbnails be of max-width X and max-height Y (the type of target options currently available) and furthermore, if it’s a document take page 1 (or maybe you need a different page in your deployment) or if it’s a video take 1 frame starting 0.5 seconds in, or if it’s a layered image file take the second layer, etc. (a list of source options).

Alas, this concept of SourceTargetTransformationOptions hasn’t yet been embraced by the Alfresco team but is used by the video transformer in the thumbnails extension which made refactoring for renditions even more difficult, but you’re not here to listen to me bitch and moan, so I’ll just say that it’s done and seems to be working fine.

So, there you have it, renditions and subsystems as they relate to video thumbnails. Hit me up with any questions or things I’ve missed.

It seems like every 6 months to never I hear: “The Alfresco thumbnails forge project used to be cool man, what happened?” Chill Winston, it’s still cool.

Now that Alfresco has a native implementation of thumbnails is the forge project still needed? Well, ‘needed’ is relative I suppose, but check out what the project gets you beyond the basic Alfresco distribution:

The thumbnails forge project was started quite a while ago (like Alfresco 0.9 or so… old school) and the first public release was put on the forge in late 2006 (which would have been around Alfresco 1.3 I guess).

The project gained the attention of the Alfresco team and they contacted me about making a few changes to bring it more inline with what they had in mind for an implementation, notably creating a public thumbnail service. Those changes were made and I continued to collaborate with Alfresco on the forge project and gave input on their implementation.

Here’s a look at some of the differences to be aware of between the old thumbnails project implementation and Alfresco’s new native thumbnails:

Concept

Pre 1.0 Versions of Forge Project

Alfresco 3 Native

The service responsible for generating and retrieving thumbnails

ThumbnailService

The generateThumbnails method would create thumbnails for
all ThumbnailSpecifications defined.

A specific thumbnail can be generated with overriding options
(possibly defined by a user in the web interface) which
are merged with the defaults of theThumbnailSpecification
(useful in defining the offset for a video thumbnail for example).

ThumbnailService

The createThumbnail and updateThumbnail
methods are given the specific TransformationOptions to
use in generating the thumbnail.

The content property from which the source data will be read
must be specified when generating the thumbnail, the default cm:content
will not be assumed.

A common size and destination mimetype for thumbnails

ThumbnailSpecification

ContentTransformers and corresponging command line options explicitly
defined in config

ThumbnailDefinition

ContentTransformer determined by ContentService
from the given TransformationOptions

The detailed resizing specifications

TransformerSpecification

The specific ContentTransformer to use and the necessary
command line options are defined

TransformationOptions

The resizing details are specified using classes containing generic
definitions (for example ImageResizeOptions used by
the ImageTransformationOptions class) which are then
translated to appropriate command line code by the ContentTransformer
found by the ContentService

The model type

tn:thumbnail

<parent>cm:cmobject</parent>

Not being of type content prevents most rules from being run on
thumbnail nodes lest we do something unnecessary and resource intensive
like extract metadata or even create another thumbnail of a thumbnail node
and prevents thumbnail nodes from being indexed or returned in a search.

cm:thumbnail

<parent>cm:content</parent>

Care must be taken to not run rules or index thumbnail nodes since they
extend content.

One suggestion has been to add the following to the thumbnail type:

<aspect name="rule:ignoreInheritedRules">

<title>Ignore Inherited Rules</title>

</aspect>

The model property name of the common size and mimetype destination definition

tn:specificationName

The specifiationName was the name of theThumbnailSpecification used to generate the thumbnail.

cm:thumbnailName

The new CreateThumbnailActionExecuter uses the user-chosenthumbnailName to retrieve theThumbnailDefinition but the relationship between theThumbnailDefinition and its thumbnailName is
not enforced by the ThumbnailService.

Default thumbnail sizes (max length/width)

SMALL

80px

JPEG

MEDIUM

160px

JPEG

medium

100px

JPEG

doclib

100px

PNG

webpreview

–

SWF

imgpreview

480px

PNG

avatar

64px

PNG

Strikethroughs represent deprecated items.

Avatar thumbnail size has nothing to do with what I can only assume is an incredibly overhyped movie about pissed off blue tree people since I haven’t been to a theater in like 10 years.

This information has been available in the thumbnails project’s 1.0 release readme but as it’s not shown by default I figured I’d post here as well.